Wire and other conductors can be coated with epoxy resins by passing a heated conductor through a fluidized epoxy powder, then through an oven, or by passing a cold, grounded conductor through an electrostatically charged powder, then through an oven. In either method, no solvent is present and, therefore, unlike enamel coatings, no heat is used to evaporate a solvent and there are no air pollution problems due to solvent vapors. Initially, however, epoxy coating powders tended to be insufficiently flexible or if flexible originally, they tended to lose their flexibility within a few days. When the coated wire was sharply bent, the inflexible insulation cracked.
While this problem has been largely overcome recently (see application cited below), the new, more flexible powders have dissipation factors, especially at higher temperatures, which are too high to permit their use in certain electrical apparatus such as some transformers.